This Demonstration shows the stationary states (eigenvalues and eigenfunctions of the Hamiltonian) for a quantum particle in one dimension under the influence of an adjustable potential. The potential is a sum of two components: (1) a power potential, symmetric for even exponent (such as the default value 2 for the harmonic oscillator) and antisymmetric for odd exponent (e.g., 1 for the inclined plane) and (2) a Gaussian potential barrier. If the barrier (you can select the height, width, and center position) is set appropriately, it turns the harmonic oscillator potential into a double-well potential, an extensively studied quantum-mechanical model system. For the stationary states, you can choose between three graphical representation modes. The most detailed information is obtained in the first of these modes, showing the potential as well as the real and imaginary parts of the eigenfunctions. You can select the stationary state to be displayed. The index shows how increasingly higher excited states change the geometrical features of the wavefunctions. You can also observe how the energy eigenvalue increases correspondingly.